Gas-liquid contacting systems exist in a wide variety of forms, depending on the function of the system, such as distillation, flashing, rectification, absorption, stripping, evaporation, humidification, and drying, and on the flow rates of gas and liquid through the system, as well as other parameters of the system. Many systems, such as ozonization systems for water, can be performed in relatively simple gas contact tanks without the need for plates, packings, or complex construction. These gas contact tanks can accommodate a high volume of water with low capital investment and low maintenance.
When treating water with ozone or any such gas that is marginally soluble in water, the critical parameters in achieving an effective treatment are (a) a high degree of mixing to maximize the contact between the gas and the water and (b) the duration of contact. Ozone is a prime example of a treatment agent where extensive mixing and an extended contact time are important in achieving effective treatment. For drinking water, the Environmental Protection Agency has established standards for the "CT" value, which is the product of the ozone concentration in the water in parts per million and the treatment time in minutes. The standard minimum value of CT ranges from 1 to 10 depending on the particular organisms to be destroyed in the water.
Contact tanks of the prior art are generally designed for counter-current flow with ozone gas bubbling up from the bottom of the tank while water enters at the top of the tank and leaves at the bottom. The contact efficiency of these tanks is approximately 50% at water depths above fifteen feet (4.6 meters) and water temperatures between 50.degree. F. (10.degree. C.) and 80.degree. F. (27.degree. C.). The low efficiency is due to a significant amount of bypass of the water flow in these tanks. As a result, the gas-liquid contact is not uniform throughout the tank and is difficult to measure or control.